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The resin characterization is a key element in the manufacturing of composite materials. Resin processing properties and their associated constitutive models are essential in order to define and optimize the processing parameters and predict the final properties of a composite structure. In this article, a comprehensive methodology is presented to characterize the main processing properties of a thermoset resin system. As a case study, the thermal, chemorheological, and thermomechanical properties of the CYCOM 890RTM epoxy resin were investigated. A cure kinetics model taking into account the diffusion was found to accurately predict resin cure kinetics behavior within the processing condition range. The developed resin rheological model accurately predicted the onset of resin gelation and the evolution of resin viscosity with temperature and degree-of-cure. The glass transition temperature and instantaneous elastic modulus were determined using also a rheometer in a solid torsion mode. Finally, volumetric changes, resin chemical shrinkage and coefficient of thermal expansion were investigated taking into account the chemical and thermal effects. In general, the detailed procedure and techniques presented in this work can be applied to the intensive characterization of a wide range of thermoset resin systems.

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The present study investigated the effects of three pressure-related process deviations (reduced ambient pressure, reduced vacuum and restricted air evacuation) on the consolidation and quality of flat laminates manufactured by out-of-autoclave prepreg processing. The evolution of laminate thickness, measured in-situ, was correlated with thickness and porosity data for woven and unidirectional fibre bed composites. The process deficiencies are shown to have had distinctive detrimental effects on the rate of thickness change and on the amount, distribution and morphology of voids, and to have been more pronounced for the woven fabric prepreg format due to its higher initial bulk factor.

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